The world depends on hydrocarbons to solve many of its energy needs. Consequently, oil field operators strive to produce and sell hydrocarbons as efficiently as possible. Much of the easily obtainable oil has already been produced, so new techniques are being developed to extract less accessible hydrocarbons. These techniques often involve drilling a borehole in close proximity to one or more existing wells. One such technique is steam-assisted gravity drainage (“SAGD”) as described in U.S. Pat. No. 6,257,334, “Steam-Assisted Gravity Drainage Heavy Oil Recovery Process”. SAGD uses a pair of vertically-spaced, horizontal wells less than 10 meters apart, and careful control of the spacing is important to the technique's effectiveness. Other examples of directed drilling near an existing well include intersection for blowout control, multiple wells drilled from an offshore platform, and closely spaced wells for geothermal energy recovery.
One way to direct a borehole in close proximity to a cased well is through the use of electromagnetic (EM) logging tools. EM logging tools are capable of measuring a variety of formation parameters including resistivity, bed boundaries, formation anisotropy, and dip angle. Because such tools are typically designed for measuring such parameters, their application to casing detection may be adversely impacted by their sensitivity to such environmental parameters. Specifically, the tool's response to nearby casing can be hidden by the tool's response to various environmental parameters, making it impossible to detect and track a cased well, or conversely making the tool produce false detection signals that could deceive the drilling team into believing they are tracking a nearby cased well when such is not the case. Such difficulties do not appear to have been previously recognized or adequately addressed.
While the invention is susceptible to various alternative forms, equivalents, and modifications, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto do not limit the disclosure, but on the contrary, they provide the foundation for supporting all alternative forms, equivalents, and modifications falling within the scope of the appended claims.